Many modern video coding strategies, such as the H.264/AVC standard, use quadtree-based partition structures for coding macro-blocks. Such a structure allows the coding algorithm to adapt to the complicated and non-stationary nature of natural images. Despite the adaptation flexibility of quad-tree partitions, a recent study by C. Dai, O. Escoda, P. Yin, X. Li, C. Gomila, “Geometry-Adaptive block Partitioning for Intra Prediction in Image & Video Coding,” Image Processing, 2007, ICIP 2007, IEEE International Conference on Volume 6, Sep. 16, 2007-Oct. 19, 2007, pp VI-85-VI-88, has shown that these are not efficient enough (in terms of rate distortion performance) when images can be locally modelled as 2D piece wise-smooth signals.
Therefore, Dai et al. investigated in said study the use of geometry based block partitioning for modeling 2D piece wise data in the macro-block. They proposed geometric partitions within blocks wherein said partitions are defined by the implicit parametric model of a line: f(x, y)=×cos θ+y sin θ−ρ. The partitioning line, generated by the zero level line of f(x, y) is determined by angle θ and distance ρ. Then, θ and ρ are encoded and transmitted in the bit-stream for blocks with mode “geo”. A gain in PSNR up to 12% was achieved, despite supplemental encoding cost of θ and ρ in Intra.
R. Mathew and D. S. Taubman described in “Joint Scalable Modeling of Motion and Boundary Geometry with Quad-tree node merging,” ICIP 2009, that the geometry model for a given sub-block in the geometry tree can be conveyed by signaling the two intercepts of the line segment with the block boundary. These two intercepts are differentially coded with reference to the boundary geometry of the parent block.
Additionally, to reduce the encoding cost of a traditional but sub-optimal quad-tree, R. D. Forni and D. S. Taubman proposed in “On the Benefits of Leaf Merging in Quad-Tree Motion Models,” Image Processing, 2005, ICIP 2005, IEEE International Conference on Image processing, Volume 2, 11-14 Sep. 2005, pp II-858-61, proposed to encode an additional binary merge flag indicating whether or not neighboring leaves have to be merged. If the leaf is to be merged, additional 0, 1 or 2 bits are coded to identify the specific merging direction. With its implementation, the authors experienced gains in PSNR between 0.5 dB to 1 dB compared to H.264/AVC.